Hello,
Are you using a POP or IMAP account in Outlook?
Open Outlook and go to File, Account Settings, Account Settings, then select your account and click Repair, follow the prompts and make sure the server settings match your email provider, then go to Send/Receive and click Update Folder, also check that Work Offline is not enabled and that your Inbox filter is set to All, finally go to File, Options, Advanced and click Send/Receive to ensure automatic send receive is enabled, these steps will reconnect Outlook to the mail server and resume email delivery.